Several lines of evidence suggest that the growth of many cancers is maintained by a small population of cancer stem cells. Cancer stem cells share properties of embryonic and adult stem cells. Indeed, cell transformation and cancer growth are controlled by the same cell-cell communication pathways used by stem cells to promote self-renewal and pluripotency. High calorie diets and increased insulin and steroid hormone levels are known to increase cancer risk. This correlation is especially important in light of the increasing obesity epidemic in the U.S. and abroad. However, the connection between these factors and tumor growth or cancer stem cell proliferation has not been clearly defined. Thus, understanding the molecular mechanisms by which normal stem cells respond to nutritionally regulated signals will yield new insights into the regulation of cancer growth. To explore these mechanisms, we use the Drosophila ovary as a model system to study the control of stem cell activity by diet. Our laboratory has demonstrated that the ovary rapidly responds to changes in diet by altering stem cell division rates, germline cell growth, and follicle cell proliferation. This process requires the direct stimulation of the germline by neural-derived insulin signals. Recent evidence from other laboratories has suggested that the effects of insulin on larval growth are counteracted by ecdysone, a steroid hormone structurally and evolutionarily related to human estrogen. Ecdysone has known roles in oogenesis, including coordination of border cell migration and follicle cell differentiation. Additionally, loss of ecdysone signaling prevents progression of egg chambers through vitellogenesis;however, it is unknown whether ecdysone signaling connects the rate of oogenesis and diet, or whether ecdysone modulates insulin signaling in the ovary. The goal of this proposal is to understand the mechanisms by which ecdysone and insulin signaling may act together to control ovarian stem cells in response to changes in diet. To test the hypothesis that ecdysone signaling modulates the insulin pathway to control the ovarian response to diet, we will use loss-of-function mutations in the ecdysone pathway to determine if ecdysone signaling is involved in the response to diet. We will also determine which cell types in the ovary receive and respond to the ecdysone signal. Lastly, we will investigate whether ecdysone signaling may antagonize or cooperate with the stimulatory effects of insulin on rates of stem cell proliferation, and probe the relevant mechanisms involved. Understanding the molecular mechanisms by which normal adult stem cells respond to diet, steroid hormones, and insulin will be highly beneficial for the development of new therapies for cancer targeted at the level of the supporting stem cells.